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2018773 
Journal Article 
The Neutralization-Flocculation-Lamellar Settling (NF-LS)process in the treatment of Acid Mine Drainage (AMD) from Coal Mines in South Brazil. Comparative processes and new basis for sulphate ion removal 
Rubio, J; Silva, R 
2010 
187-190 
WOS:000323234800040 
Coal mining activities readily generate acid wastewaters after contacting pyrite with air and water (superficial or subterranean) resulting in AMD-Acid Mine Drainage, loaded with heavy metal ions at pH < 3. This paper summarizes results of treatment processes composed of neutralization-flocculation (NF) and flocs/water separation in lamellar settler (LS) or by flotation with microbubbles (DAF-dissolved air flotation). Furthermore, the works presents a new basis for sulphate ions removal by co-precipitation of this pollutant with aluminum salts. Two AMD from different coal mines were used as models, characterized by their content, namely inorganic or organic elements, suspended and dissolved solids, among others. After neutralization of the AMD, the precipitates are then flocculated using a cationic polymer flocculant in a specially designed flocculation reactor, patented by this research group (FGR (R)). The separation of flocs in a settler (neutralization-flocculation-lamellar settling-NFLS) showed a high efficiency (>90%) in removal of ions, lower power requirement and process simplicity than when DAF was used. Flocs settled at rates of the order of 5-6 m.h-1 and operating costs for the AMD treatment at pH g were estimated to be around $ 0.3.m(-3). The treated water was nearly free of heavy metals ions, low BOD and TOC, low solids content and no fecal coli forms, making it useable for irrigation, and other purposes. It is concluded that this research will contribute in the discussion of this old and complex problem in acid mining effluents worldwide. Sulphate ions are, in one case precipitated, at pH 12, in the form of ettringite (3CaO center dot 3CaSO(4)center dot Al2O3 center dot 31H(2)O) formed in situ after reaction with Ca/Aluminum salts. The solid formed was separated off by DAF process. Results showed residual concentrations of sulphate ions lower than 250 mg.L-1 and almost go% removal of ions and solids. Sulphate ions removal in acid medium (pH 4.5) is currently underway and initial results were quite high after co-precipitation-filtration with aluminum salts and solids separation either by LS or DAF. 
Acid Mine Drainage; lamella settler; sulphate ions; water reuse